1. Field of the Invention
The invention relates to a brake control system and a brake control method which controls the braking force applied to a wheel of a vehicle.
2. Description of the Related Art
Japanese Patent Application Publication No. 2004-322843 (JP-A-2004-322843), for example, describes one electronically controlled brake system that controls the braking force to each wheel in such a manner as to apply the optimal braking force for the running state of the vehicle to the vehicle. This electronically controlled brake system monitors the wheel cylinder pressure in each wheel using pressure sensors, and controls an electromagnetic flowrate control valve such that the wheel cylinder pressure matches a target pressure calculated based on a brake pedal operation amount by a driver.
Incidentally, Japanese Utility Model Application Publication No. 7-35228 (JP-U-7-35228) and Japanese Patent Application Publication No. 2000-272497 (JP-A-2000-272497) describe electronically controlled brake systems that have a fluid level detecting apparatus that detects when the level of fluid in a reservoir has become lower than a preset fluid level. When this fluid level detecting apparatus detects that the fluid level has become lower than the set fluid level, it is determined that there is a fluid leak and a warning is issued to the driver and the wheel cylinder pressure control mode is changed.
In this electronically controlled brake system, it is necessary to ensure that the reservoir has a capacity large enough to enable the fluid level detecting apparatus to operate. If the reservoir capacity is too small, there may not be enough fluid for the fluid level detecting apparatus to operate due to variations in the amount of fluid filled when the vehicle is shipped from the factory or compression of the fluid due to changes in the temperature in the engine compartment or the like. Moreover, if the fluid level is low, the fluid level detecting apparatus may activate and the hydraulic control mode may end up being changed even if the reason for the fluid level being low is because of worn brake pads and not a leak.
Normally an electronically controlled brake system is configured such that if a fluid leak is detected, the control mode is switched to a failsafe mode in which fluid in the master cylinder is supplied directly to the wheel cylinder. In this failsafe mode, the braking force is less than it is in the control mode during normal operation so it is not preferable to change the control mode often due to an erroneous leak determination.
However, in compact vehicles and the like, it is sometimes difficult to provide a reservoir having a large enough capacity due to the issue of space in the engine compartment. Also, in recent years, there is a demand to ensure sufficient space between the hood of the engine compartment and the reservoir in order to protect pedestrians in the event of a vehicle crash, so it is becoming increasingly difficult to provide a reservoir with a large enough capacity to prevent erroneous leak determinations.